Effects of Pirin-like proteins on PAT biosynthesis and stress resilience in postharvest apple pathogen Penicillium expansum.

Penicillium expansum is a predominant postharvest pathogen that causes blue mold on pome fruits and produces PAT. Pirin proteins, belonging to the Cupin superfamily, have been found in a variety of organisms and have a multitude of functions. However, the Pirin-like proteins in P. expansum have not been identified and functionally studied. In this study, we screened and identified two Pirin-like proteins in P. expansum (Pepirin1 and Pepirin2). Pepirin1 was localized in mycelial septa and conidia, while Pepirin2 was mainly localized in cytoplasm. The growth and pathogenicity of P. expansum were characterized through knockout and complementation of Pepirin1 and Pepirin2. Although deletion of these genes had no significant effect on fungal growth or pathogenicity, it did lead to increased sensitivity to osmotic and oxidative stress. Moreover, compared with the WT, ΔPepirin1 and ΔPepirin2 showed a significant reduction in the patulin accumulation, correlating with a significant down-regulation of key genes for patulin biosynthesis (PatG, PatH, PatN). In addition, Pepirin1 has no quercetinase activity. All these results suggest that Pepirin proteins play important roles in patulin biosynthesis and osmotic and oxidative stress responses in P. expansum.